Fibers enter a practical stage as multimode fibers emerge. In recent years, for single-mode fibers, new varieties continue to emerge, functions are increasingly enriched and enhanced, and the cost performance continues to improve, but multimode fibers cannot be replaced and still maintain a stable market share. The reason is that a multimode fiber has many features satisfying requirements on a local area network (LAN) fiber that the single-mode fiber does not have.
Compared with a long-distance trunk, a LAN fiber network has the following features: the transmission rate is relatively lower; the transmission distance is relatively shorter; but the numbers of nodes, connecting points, bent paths, and connectors and couplers used are large, the overall scale of use is small, and the number of light sources consumed per unit distance of fiber is large. The low transmission rate and the short transmission distance may be addressed with bandwidth features of the multimode fibers and the feature that transmission losses of the multimode fibers are less than that of the single-mode fibers. The single-mode fibers are cheaper, and have better performance than the multimode fibers, but why the single-mode fibers are not used in an access network? The reason is that in this type of networks, the number of bent paths is large and the loss is large; the large number of nodes results in frequent optical power division, which requires that the interiors of the fibers have sufficient optical power transmissions. Compared with the single-mode fiber, the multimode fiber has a larger core diameter and a larger numerical aperture, and can couple more optical power from a light source. In a network, the number of consumed connectors and couplers is large. Unusually, passive devices of the single-mode fibers are more expensive than that of multimode fibers, are also more delicate, but are not as convenient and reliable as multimode devices during operation. A more important difference lies in that the single-mode fibers can only use a laser diode (LD) as a light source, and the LD is much more expensive than an LED usually used by the multimode fiber. Especially, for a LAN, the network size is small, and when the number of light sources consumed per unit distance of fibers is large, if the single-mode fibers are still used in combination with single-mode fiber LDs, the cost of the LDs becomes the major part of the overall cost of the network. Therefore, although the single-mode fibers are cheaper than the multimode fibers, the high prices of the LDs and the connectors that are the major part of the cost still dramatically increase the overall cost.
According to the standards recommended by international standards organizations such as the IEC and the ITU, conventional multimode fibers may be classified into two categories, namely 50 μm and 62.5 μm. The 50 μm category may be further classified into OM2, OM3, and OM4 types, according to the bandwidths. Light gathering capability of the fibers is indicated by the numerical aperture of the fibers. Normally, the numerical aperture of a 50 μm multimode fiber is 0.20, while the numerical aperture of a 62.5 μm multimode fiber is 0.27. Recently, in order to meet requirements of access network applications and data centers on fiber bending radius, bending resistance performances of the conventional multimode fibers have been improved, thereby resulting in bending-resistant OM3 and OM4 fibers. However, the existing multimode fibers still cannot fully meet high bandwidth requirements of data transmissions.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.